At present there are known bearings of the above mentioned kind, in particular tapered roller bearing units, provided with a sensor screwed in a threaded radial bore formed in the radially outer, stationary race of the bearing. The sensor is located facing an encoder wheel which is fast for rotation with the radially inner, rotating race of the bearing and axially interposed between two sets of tapered roller elements, as shown in the axial cross sectional view of FIG. 1. Referring to this drawing, a wheel hub bearing unit comprises a hub 10 forming a radially outwardly projecting flange 11 provided with axially oriented bores 12 for fitting fastening members 13 for connecting to the wheel of the vehicle (not shown). The hub is fitted with a rolling contact bearing comprised of a radially outer stationary race 14, a pair of radially inner, axially flanked rotating half-races 15a, 15b, and two sets of tapered rollers 16a, 16b, radially interposed between the outer race 14 and the two inner half-races 15a, l5b, respectively. An encoder wheel 17 is fixed for rotation between the inner half-races 15a and 15b. Facing the encoder wheel 17 is a sensor 18 screwed in a bore 19 formed in the stationary, outer race 14 and oriented substantially radially.
This known solution, that on one side is advantageous in that the sensor is interchangable, has nevertheless some drawbacks.
Firstly, a problem arises in having to perform a substantially radial bore in the outer race of the bearing, as this kind of operation requires special drilling machinery that is not installed in present bearing processing lines. Further, the execution of the bore is complicated in that this operation also affects the hardened zones of the races. Also, the bore for accommodating the sensor must be performed and located precisely to prevent the sensor from contacting the encoder wheel that it is facing, but still the sensor has to be near enough to the encoder so as to be able to detect the magnetic pulses or magnetic field variations generated by the rotation of the encoder. Another inconvenience related to said prior art arrangements is that, in order to accommodate the encoder wheel between the two sets of tapered rollers, the relevant races have to be suitably spaced apart, whereby the bearing is considerably bulky in the axial dimension.